He is simply answering a question on when you call something terrorism.
Nice attempt to make political gain from the tragedy.
Whether or not something is terrorism often hinges on motive. For example, Adam Lanza was a mass murderer, many would not call him a terrorist.
Axelrod is saying this event could be attributable to one of many motives, even the fact that it was tax day. He clearly says we do not know yet. Given the nature of the attack , it probably had a political motive and therefore is called terrorism.
It's not clear to me why using the term "terror" immediately is important. Obama said it the day after Benghazi and still people tired to act like he didn't. Romney faceplanted in the debate because of the echochamber effect that led him to believe it had not been said. it culminated with the "please proceed, governor" moment.
What is important is figuring out who did it and why.